In the manufacture of semiconductor integrated circuits, the semiconductor wafers (typically silicon) subjected to a variety of processing steps at one or more workplace (horizontal) surfaces. During the course of such manufacture, undesirable electrostatic charges of either polarity tend to build up at various locations of the workplace surface proximate to the wafers, whereby the resulting electrostatic fields at the wafers cause undesirable damage to components of the wafers and thus undesirably reduce the yield of operable circuits, for example, by damaging fragile insulating layers embedded in transistor structures within such circuits in the wafers. In addition, electrostatically charged ambient dust particles undesirably tend to cling by electrostatic attraction to exposed surface of the wafers. Such dust particles introduce deleterious defects into the circuits during further processing, so that the yield of oeprable circuits is further undesirably reduced.
In prior art, in order to neutralize such electrostatic charge buildup, workers have injected showers of positive and negative ions into a region located above the workplace from points of metal needles located above the workplace, either by applying to the needles an AC voltage of about 60 cycles so as to produce alternating showers of positive and negative ions from the points of the needles, or by applying a steady DC voltage of positive polarity to some of the needles and a steady DC voltage of negative polarity to the other needles so as to produce simultaneoulsy a steady shower of positive ions and a steady shower of negative ions. In either case, the resulting ions of positive and negative polarity tend to neutralize any buildup of electrostatic charge at the workplace, especially when the showers are sided by a downward airflow coming from above the locations of th eneedles. However, the time it takes in either case (AC or DC) for this neutralizing electrostatic charge buildup at the workplace is unduly long, probably because of the recombination of too many of the positive and negative ions before they reach the workplace surface, and accordingly the suppression of electrostatic charge buildup at the workplace surface is not as effective as desired.
It would, therefore, be desirable to have a method for more effectively suppressing electrostatic charge buildup at a workplace and hence for improving the yield of operable semiconductor integrated circuit wafers that are processed thereat.